Low profile polyester molding composition

ABSTRACT

Dimensionally stable, pigmentable polyester molding compositions comprise: 
     A. polymerizable polyester component; and 
     B. an additive component comprising discrete particles of less than about 50 microns diameter of a lightly cross-linked vinyl chloride polymer having a glass transition temperature of below about 100° C and which is chemically inert with respect to the polyester component and is swellable but insoluble therein. 
     The additive component is a vinyl chloride polymer or copolymer lightly cross-linked with a suitable polyfunctional monomer, such as a diacrylate.

BACKGROUND OF THE INVENTION

This invention relates to polyester molding compounds and additivestherefor characterized by uniform pigmentability and dimensionalstability.

For many years polyester resins based on an unsaturated polyester and anunsaturated monomer, such as styrene, have been used in the preparationof molding compositions. When formulated in a known manner withappropriate adjuvants such as fillers, pigments, curing agents,reinforcing agents, and the like, such polyester-based moldingcompositions may be used in conventional molding processes such as sheetmolding or bulk molding to prepare a wide variety of materials orarticles which are generally characterized by high strength, lightweight and excellent chemical resistance. However, articles fabricatedfrom such molding compositions by conventional molding techniquescommonly exhibit poor dimensional stability, due in a large part toshrinkage during the molding process. The poor dimensional stability istypically evidenced by a rough or warped surface (high profile) andsurface irregularities such as deep sink marks opposite structural ribs.Thus, considerable difficulties are encountered in the production ofmolded articles where close size and shape tolerance limits are requiredsince in many instances an inordinate amount of labor is required afterremoval of a part from the mold to shape it to the exact finish, size orshape required for a given application.

Considerable effort has been expended in recent years, in thedevelopment of dimensionally stable (low-profile) polyester moldingcompositions. It is now well known to those skilled in the art that withthe addition of thermoplastic polymers to polyester systems, such aspolyester-styrene based resins, there may be prepared compositionswhich, when formulated with the appropriate adjuvants to form moldingcompounds, display minimal shrinkage or expansion during the moldingprocess and may be formed with smooth surfaces (low-profile). Thethermoplastic polymers which have been used for this purpose include,for example, such materials as polyvinyl acetate, cellulose acetate,cellulose butyrate, polymethyl methacrylate, polystyrene, polyethylene,polyvinyl chloride and saturated polyesters.

With the advent of low-profile unsaturated polyester systems, moldingtechniques have been increasingly employed in the fabrication ofautomotive parts such as hood scoops, fender extensions and a widevariety of other parts which require both a smooth surface and closeadherence to the size and shape of a precision machined mold.

In the production of articles such as automotive parts, it isparticularly desirable to impart the desired color to the articles byaddition of a pigment to the molding compound prior to the moldingprocess. This technique eliminates the need for an additional coatingstep after molding, and in general, minimizes maintenance and extendsthe useful life of the article since the color is dispersed throughoutthe material rather than only on the surface. However, it has been foundthat, in low profile unsaturated polyester molding compounds containingthermoplastic additives, the achievement of uniform coloration isdifficult at best. The addition of a thermoplastic polymer, with theexception of polyethylene and polystyrene, to an unsaturated polyestermolding compound, results in a non-uniform distribution of the pigmentand a "phase out" or separation of non-pigmented and pigmented areasduring molding or curing. The result is an undesirable mottledappearance of the surface. When polyethylene or polystyrene is employedas the thermoplastic polymer additive, considerable improvement in theuniformity of pigmentation is achieved. However, the dimensionalstability, although improved by the addition of polyethylene orpolystyrene is notably less than that achieved with other thermoplasticpolymer additives, which phase out during molding or curing. Thus amanufacturer utilizing molding compounds which incorporate thermoplasticpolymer additives must choose between a thermoplastic polymer whichimparts good surface smoothness and dimensional stability, but whichcannot be pigmented uniformly, and a thermoplastic polymer which impartsgood pigmentability but is substantially poorer in surface smoothnessand dimensional stability.

Accordingly, it is an object of the present invention to provideunsaturated polyester based molding compositions which exhibit a highdegree of dimensional stability. It is a further object to providelow-profile additive compositions which may be added to unsaturatedpolyester based molding compositions to impart a high degree ofdimensional stability thereto without adverse effect on thepigmentability of the composition. It is a still further object toprovide a method for the production of molded articles from unsaturatedpolyester based molding compounds, wherein the molded articles areuniformly pigmented and are within close tolerance limits of the sizeand shape imparted by the mold. It is an additional object to providearticles of manufacture molded from novel polymeric compositions andhaving uniform pigmentation and closely reproducible size and shape.

SUMMARY OF THE INVENTION

It has now been found that polyester molding compositions havingexcellent pigmentability and dimensional stability comprise (A) apolymerizable polyester component; and (B) an additive componentcomprising discrete particles of less than about 50 microns diameter ofa cross-linked vinyl chloride polymer having a glass transitiontemperature (Tg) of below about 100° Celsius and which is chemicallyinert with respect to the polyester component and is swellable butinsoluble therein, the additive component comprising the polymericreaction product of vinyl chloride and at least one polyfunctionalmonomer.

The low profile polyester molding compositions of this invention arecharacterized by dimensional stability, that is smooth surfaces andlittle or no shrinkage during molding and curing, as well as uniformityof pigmentation or evenness of color in the final molded article.

The present invention may be considered in terms of three major aspectsthereof:

a. novel low profile additives which may be incorporated intounsaturated polyester molding compositions to impart dimensionalstability thereto without adverse effect on pigmentability;

b. unsaturated polyester molding compositions containing novel lowprofile additives; and

c. molded articles of manufacture prepared therefrom.

Although the unsaturated polyester molding compositions are described interms of major components thereof, that is the unsaturated polyestercomponent and the additive component, it will be appreciated that, inaccordance with known practice, the molding composition may also includeadditional appropriate ingredients including, for example, fillers,lubricants, pigments, fire retardants, curing agents, reinforcingagents, mold release agents, and the like. The molding compositions ofthis invention may be uniformly pigmented with organic or inorganicpigments. Pigments for the coloration of the polymer molding compoundsmay be employed as a powder or as a paste or dispersion in a vehiclethat is compatible with the type of polymer to be pigmented. Thus, forexample, pigments formulated as a color paste or dispersion in apolyester resin vehicle compatible with polyester resin compositionssuch as those of the present invention may be employed. However, ifdesired, a pigment per se or a pigment dispersed in various othervehicles compatible with polyester resins may be employed. In oneembodiment, the pigment alone, or as a paste or dispersion, may beadmixed with the additive component of this invention prior toincorporation in the polyester molding composition.

DESCRIPTION OF EMBODIMENTS The Polyester Component

The polymerizable polyester component of the molding compositions ofthis invention comprises an unsaturated polyester and preferably, inaddition, a copolymerizable unsaturated monomer.

The unsaturated polyesters which may be employed include those commonlyknown in the art, and are generally the reaction product of apolycarboxylic compound and a polyhydric alcohol. The preferredpolycarboxylic compounds and polyhydric alcohols are dicarboxyliccompounds and dihydric alcohols. Carboxylic compounds and alcoholshaving a functionality greater than two may be employed, usually inminor amounts. In such cases it may be advantageous to incorporate acompensatory amount of monofunctional acid and/or alcohol to controlmolecular weight and gelation as desired. By polycarboxylic compounds ismeant the polycarboxylic acids, polycarboxylic anhydrides,polycarboxylic acid halides, and polycarboxylic acid esters. Theunsaturation can be provided in either or both the polycarboxyliccompound or the polyhydric alcohol. Suitable unsaturated polycarboxylicacids having aliphatic carbon-to-carbon doube bonds, and thecorresponding acid halides, esters, and anhydrides can include forexample, maleic, fumaric, chloromaleic, ethyl-maleic, itaconic,citraconic, mesaconic, aconitic and acetylene dicarboxylic, and the likeeither alone or in mixtures.

Illustrative of the unsaturated polyhydric alcohols having aliphaticcarbon-to-carbon double bonds, which can be used in providing theunsaturation in the linear polyester molecules are compounds such asbutene diol, pentene diol, the unsaturated hydroxy ethers such as allylor vinyl glycerol ethers, allyl or vinyl pentaerythritol ethers and thelike and mixtures thereof.

The saturated polycarboxylic compounds useful in the preparation of thepolyesters can be aliphatic, cycloaliphatic, aromatic or heterocyclic.Illustrative of these polycarboxylic acids, acid halides, acidanhydrides and acid esters include phthalic, isophthalic, terephthalic,tetrachlorophthalic, tetrabromophthalic, dibromotetrahydrophthalic,chlorenic, adipic, succinic, dichlorosuccinic, and the like and mixturesthereof.

Suitable saturated polyhdric alcohols for use in the preparation of thepolyester resins include ethylene glycol, diethylene glycol, propyleneglycol, dipropylene glycol, butane diol, pentane diol, hexane diol,dibromoneopentyl glycol, 1,4-cyclohexane dimethanol, glycerol, mannitol,sorbitol, bisphenols, substituted bisphenols, hydrogenated bisphenolsand mixtures thereof.

The properties of the polyester resins can be modified by theincorporation of suitable monofunctional carboxylic compounds andalcohols. Illustrative examples of such compounds are2,2-dichloroethanol; 1,1-dibromo-2-propanol; 2,2,2-tribromoethanol;1,1,3,3-tetrabromo-2-propanol; 1,1,1-trifluror-2-propanol and2,3-dibromo-1-propanol. An example of a carboxylic compound ispentachlorophenoxy acetic acid.

The properties of the polyesters can be varied by using mixtures of thevarious types of acids and alcohols, such as an unsaturated acid, asaturated acid and an saturated alcohol.

The temperature for the reaction between polyhydric alcohols andpolybasic acids ranges from about 100° to 200° C., although higher orlower temperatures can be used. Esterification catalysts such aspara-toluene sulfonic acid, benzene sulfonic acid, betanaphthalenesulfonic acid and the like, or amines such as pyridine, triethyl amine,quinoline and the like can be added to the reaction mixture. Theproportion of polyhydric alcohol is approximately controlled by thetotal mole proportion of acids in the esterification reaction mixture.It is also preferred to react the polyhydric alcohols and polybasicacids in roughly equimolar proportion; however, either the acids oralcohols can be used in substantial excess, if it is desired to form alow molecular weight polyester resin.

The aforementioned unsaturated polyesters and components thereof areintended to be illustrative of polyesters suitable for the compositionsof this invention and are not intended to be all-inclusive. Themolecular weight of the polymerizable unsaturated polyester is notcritical and may vary over a wide range. Typically, the averagemolecular weight will be in a range of from about 500 or less to about10,000, or higher and preferably from about 700 to about 6000.

A variety of ethylenically unsaturated copolymerizable monomers can beused for curing or cross-linking the ethylenically unsaturatedpolyesters. The monomer is preferably liquid at reaction temperatures,has the ability to dissolve the unsaturated polyester and iscopolymerizable therewith to form a cross-linked structure. Suitablemonomers are generally characterized by the presence of at least onereactive H₂ C═C group per molecule. Specific examples of such monomersinclude styrene, chlorostyrenes, methyl styrenes such as alpha methylstyrene, p-methyl styrene, vinyl benzyl chloride, divinylbenzene,indene, fluorostyrene, unsaturated esters such as methyl acrylate,methyl methacrylate, as well as other lower aliphatic esters of acrylicand methacrylic acids, allyl acetate, diallyl phthalate, diallylsuccinate, diallyl adipate, diallyl sebacate, diethylene glycol bis(allyl carbonate), triallyl phosphate and other allyl esters, and vinyltoluene, diallyl chlorendate, diallyl tetrachlorophthalate, ethyleneglycol diacrylate, ethylene glycol dimethacrylate, ethylene glycoldiethacrylate and the like and mixtures thereof.

The proportion of unsaturated monomer to unsaturated polyester can varywithin the ultimate limits of each as necessary to produce an infusible,insoluble polyester resin. Generally the weight proportion ofunsaturated monomer:unsaturated polyester will be between about 0.1 and9.0 and preferably between about 0.25 and 7.5, part of monomer per partof polyester.

Polymerization catalysts are preferably added to the mixture ofunsaturated polyester and unsaturated monomer to effect setting orcuring. Catalysts such as benzoyl peroxide, acetyl peroxide, lauryolperoxide, methylethyl ketone peroxide, cumene hydroperoxide, and thelike are satisfactory. Such catalysts are commonly used in proportionsof about 0.01 to 10 weight percent of the resin, depending on theefficiency of their action and whether or not substances which inhibitpolymerization are present in the mixture.

For convenience in handling and mixing, a portion of the monomer may becombined with the unsaturated polyester, to serve as a solvent thereforprior to the addition of the low profile additive or other compoundingingredients and the remainder of the monomer may then be added duringthe formulation of the molding compound. To prevent prematurepolymerization during the initial mixing of the unsaturated polyesterand a portion of the monomer, a polymerization inhibitor isadvantageously added to the mixture or to one of its components prior tomixing, especially if the polyester-monomer solution is to be stored orshipped in commerce prior to final compounding or molding and curing.Polymerization inhibitors are generally added in amounts of about 0.001to 1 weight percent of the mixture. Among the inhibitors which may beadvantageously employed to prevent premature polymerization of themixtures of unsaturated polyester and monomer are substances such ashydroquinone, toluhydroquinone, benzoquinone, para-tertiarybutylcatechol, para-phenylene diamine, trinitrobenzene, picric acid and thelike.

The Additive Component

The additive component of the present invention comprises discreteparticles of a lightly cross-linked vinyl chloride polymer having aglass transition temperature below about 100° C. and which is chemicallyinert with respect to the polymerizable polyester component and isswellable but insoluble therein. The particles are preferably of a sizerange averaging less than about 50 microns and most preferably less thanabout 25 microns in diameter to as small as 0.1 microns or less with theonly lower limit being that imposed by the difficulty of preparingdiscrete particles of smaller diameter. Based on ease and economy ofpreparation as well as achievement of low profile characteristics andpigmentability in the final product, a preferred particle size is about3 microns to about 25 microns. Particles having a diameter of less thanabout 50 microns may be prepared in a known manner, for example, byemulsion or suspension polymerization techniques. Larger size particlesmay be reduced in size by mechanical methods such as pulverization.

The lightly cross-linked vinyl chloride polymer comprises the polymerreaction product of vinyl chloride and at least one polyfunctionalmonomer, the functional groups of which are carbon to carbon doublebonds capable of radical polymerization. Suitable polyfunctionalmonomers which may be employed for this purpose include, for example,1,3-butylene glycol diacrylate; 1,3-butylene glycol dimethacrylate;1,4-butylene glycol diacrylate; 1,4-butylene glycol dimethacrylate;1,10-decamethylene glycol diacrylate; 1,10-decamethylene glycoldimethacrylate; ethylene glycol diacrylate; ethylene glycoldimethacrylate, diethylene glycol diacrylate; diethylene glycoldimethacrylate; 1,2 propylene glycol diacrylate; 1,2-propylene glycoldimethacrylate; 1,3-propylene glycol diacrylate; 1,3-propylene glycoldimethacrylate; pentaerythritol tetra acrylate; pentaerythritoltetramethacrylate; 1,6-hexanediol diacrylate; 1,6-hexanedioldimethacrylate; divinyl benzene; diallyl phthalate; diallyl maleate;diallyl fumarate; allyl acrylate; allyl crotonate; divinyl acetal;divinyl formal; divinyl butyral; and the like, or mixtures thereof. Thepolyfunctional monomer is preferably employed in minor amounts of about0.1 to about 10 and most preferably about 0.3 to about 5 percent byweight based on the weight of the final cross-linked polymer.

It is important that the lightly cross-linked vinyl chloride polymerthat serves as the low profile additive component in accordance withthis invention have a glass transition temperature of below about 100°C. and preferably of about -10° to about 75° C. Particles having a glasstransition temperature of less than about -10° C may exhibit astickiness or tendency to agglomerate to an undesirable degree resultingin some uneveness of color in the final molded article. Particlescharacterized by a glass transition temperature above about 100° C.often exhibit insufficient thermal expansion to control dimensionalstability.

The homopolymer of vinyl chloride is characterized by a glass transitiontemperature of about 80° C. However, when vinyl chloride iscopolymerized with a polyfunctional monomer (cross-linking monomer) theresultant polymer will be characterized by a glass transitiontemperature higher than that of the homopolymer, depending on the amountof polyfunctional monomer employed. Thus, to obtain a cross-linkedpolymer of vinyl chloride having a glass transition temperature belowabout 100° C, wherein vinyl chloride is the sole monofunctional monomer,it is preferred to employ a limited amount, such as about 0.1 to about2.0 percent by weight of polyfunctional monomer, based on the weight ofthe final cross-linked product.

Alternatively, in a preferred embodiment, and additional monofunctionalcomonomer, or mixture of comonomers may be employed to obtain across-linked polymer having a lower glass transition temperature.Suitable comonomers which may be employed for this purpose aremonofunctional monomers, the functional group of which is a carbon tocarbon double bond capable of radical polymerization, and which arecapable of forming a linear homopolymer having a glass transitiontemperature below that of the vinyl choride homopolymer (Tg about 80°C). The incorporation of such a comonomer will serve to lower the glasstransition temperature of the resultant polymer. The preferredcomonomers for this purpose are those capable of forming linearhomopolymers or copolymers having a glass transition temperature ofbelow about 0° C. Suitable comonomers include for example, ethylacrylate, butyl acrylate, 2-ethylhexyl acrylate, n-octyl methacrylate,isodecyl methacrylate, lauryl methacrylate, tridecyl methacrylate,2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, 2-butoxyethyl acrylate,2-methoxyethyl methacrylate, ethoxyethyl methacrylate, and the like, ormixtures thereof. The most preferred monofunctional comonomers which maybe employed in combination with vinyl chloride are ethyl acrylate,n-butyl acrylate and 2-ethylhexyl acrylate. Although the amount ofcomonomer which may be employed is not critical except with respect tothe obtainment of a polymer leaving a desired glass transitiontemperature, it is preferred to employ a comonomer in amounts of lessthatn about 40 weight percent based on the total cross-linked polymeradditive component.

The lightly cross-linked vinyl chloride polymer is advantageouslyprepared from monomers such as those described hereinabove with the aidof a suitable catalyst such as a peroxide type catalyst. Typicalcatalysts include, for example, benzoyl peroxide, lauroyl peroxide,caprylyl peroxide, acetyl peroxide, t-butyl perbenzoate, t-butylperoctoate, and the like.

The uniformity of pigmentation in the final molded article will varysomewhat depending on the shape of the low profile additive particles.For maximum uniformity of pigmentation it is preferred that the additiveparticles be discrete, that is non-agglomerated particles, and besubstantially spherical in shape. However, good pigmentation is obtainedwith elongated, rounded particles. When the low profile additiveparticles are highly irregular in shape or when substantialagglomeration of particles occurs a tendency toward mottled ormarbleized appearance may result in the final product. Emulsion orsuspension polymerization methods are advantageously employed in thepreparation of small, discrete, substantially spherical or roundedpolymer particles, although other methods such as solution-precipitationpolymerization, or bulk polymerization and subsequent pulverization ofthe polymeric product, may be employed.

The preferred method is suspension polymerization which may be carriedout in a known manner by heating and stirring the monomeric reactants inwater in the presence of a suitable catalyst, such as benzoyl peroxideor lauroyl peroxide and a suitable suspension agent such as calciumphosphate or hydroxypropyl methylcellulose.

The control of shrinkage during the molding process and the resultantlow profile of the final molded article results from the use of across-linked vinyl chloride polymer additive that is swellable in theunsaturated polyester composition but substantially insoluble therein.It is known that the degree to which a polymer swells in a solvent aswell as the solubility of the polymer is dependent on the degree ofcross-linking present in the polymeric structure. Thus, to achieve thedesired control of shrinkage during the molding process the polymeradditive of this invention comprises a vinyl chloride polymer orcopolymer that is lightly enough cross-linked so that it is swelled inthe unsaturated polyester composition but sufficiently cross-linked sothat it does not dissolve therein. The degree of swelling of a polymermay be determined with the use of the known formula and procedure asfollows: ##EQU1## (See L. H. Sperling and E. N. Mihalakis, J. AppliedPolymer Science 17, 3811, (1973)).

Using the above formula the following test is employed to determinepercent swelling:

Approximately 4 grams of polymer is weighed into a Soxhlet extractionthimble and placed in an extraction apparatus. Toluene (200 ml) isvigorously refluxed so that there is a steady return of fresh solventthrough the polymer. After two hours, the thimble is removed and surplussolvent allowed to drain off by leaving the thimble to stand in a glassfunnel for 10 minutes. The polymer is then weighted and the percentswelling is calculated using the above formula.

Based on the swelling index (percent swelling) formula and testdescribed hereinabove, it has been found that lightly cross-linkedpolymers, suitable for use as low profile additives in accordance withthe present invention are preferably characterized by a swelling indexof about 200 to about 600%.

The amount of additive component which may be incorporated in thepolyester molding composition may vary considerably. To achieve optimumcontrol of dimensional stability and uniform pigmentability of the finalproduct, it is preferred to employ about 5 to about 45 and mostpreferably about 10 to about 25 parts by weight of additive componentper 100 parts by weight of polyester component.

The following specific examples are provided to further illustrate thisinvention and the manner in which it may be carried out. It will beunderstood that the specific details given in the examples are providedfor purpose of illustration and are not to be construed as a limitationon the invention. In the examples, unless otherwise indicated, all partsand percentages are by weight and all temperatures are in degreesCelsius.

EXAMPLE 1

A pressure reactor was charged with 60 parts of 2-ethylhexyl acrylate,0.6 parts of 1,3-butylene diacrylate, 0.6 parts of diallyl maleate, 700parts of water, 0.5 parts of sodium lauryl sulfate, about 50 parts of a2 percent aqueous solution of hydroxypropyl methylcellulose, 0.2 partsof acetyl cyclohexane sulfonyl peroxide, and 0.5 parts ofdi(d-ethylhexyl) peroxidicarbonate. The reactor was cooled in anice-water bath and twice pressurized with nitrogen and then evacuated.Then 350 parts of vinyl chloride was added. The reaction mixture wasstirred to form a suspension, then heated, with the aid of a warm waterjacket, to 65° C at 130 pounds per square inch for 5 hours. At the endof the reaction period the reactor was cooled and excess vinyl chloridevented. The reaction product was filtered and washed, first with 3000parts of water, then with 400 parts of methanol, then dried. The driedproduct was passed through a 20 mesh screen. The resultant powder wasexamined under a scanning electron microscope and formed to consist ofspherical particles having a diameter of about 20 microns, with veryslight agglomeration in clusters up to about 100 microns. The polymerhad a chlorine content of 47.5 percent. The glass transition temperatureof the cross-linked polymer was 75° C. The swell index of the particles,determined in the manner described hereabove, was 530 percent.

EXAMPLE 2

An unsaturated polyester was prepared by esterification of 1.05 molespropylene glycol with 0.90 moles of maleic anhydride and 0.10 moles ofphthalic anhydride to an acid number of 35. A 65 percent solution ofthis polyester in styrene was prepared.

EXAMPLE 3

A bulk molding compound was prepared, molded and tested in the followingmanner: a dispersion was prepared of 15 parts of the cross-linkedpolymer of Example 1 in 55 parts of the unsaturated polyester solutionof Example 2 and 30 parts of additional styrene. To this dispersion wasadded 3 parts of a red pigment paste (CM 7106, Pasticolor, Inc.,Ashtabula, Ohio), 3 parts of calcium stearate and 0.8 parts of2,5-dimethyl-2,5-bis (2-ethylhexanoylperoxy) hexane and 1.5 parts ofmagnesium hydroxide. The mixture was transferred to a sigma blade mixerand 200 parts of ground calcium carbonate and 75 parts of OCF 832 1/4-inch glass fiber (Owens-Corning Fiberglass) was added with mixing. Themolding compound, thus prepared, was stored in a plastic bag at roomtemperature for 48-72 hours before molding.

Two hundred and eighty parts of the molding compound was charged into an8 × 8 inch mold containing a 1/8 × 5 inch rib and a 3/8 × 41/2 inch riband molded at 121° C and 1500 pounds per square inch for 2 minutes

The molded panel had a uniform red color with a shrinkage of -0.38 milsper inch (expansion) perpendicular to the ribs and 0.00 mils per inchparallel to the ribs. Surface profile measured with a BendixMicrocorder, was 180 microinches per half inch averaged over a 2 inchspan in the center of the panel and 267 microinches per half inch overthe 3/8-inch rib. The molded panel had a Barcol hardness of 51.

EXAMPLE 4

A cross-linked vinyl chloride polymer was prepared following thesuspension polymerization procedure of Example 1, except that in placeof the monomer composition shown (vinyl chloride, 2-ethylhexyl acrylate,1,3-butylene diacrylate and diallyl maleate monomers), there wasemployed 435 parts of vinyl chloride and 1.5 parts of diallyl maleate.The resultant polymeric product, consisted of 409 parts of a finepowder. The powder was examined under a scanning electron microscope andfound to consist of spherical particles having a diameter of 20 to 50microns. The glass transition temperature of the cross-linked polymerwas 86.5° C (taken as the mid-point of a range of 82° to 91° C). Theswell index of the particles, determined as described hereinabove, was380%.

The powdered polymer, thus prepared, was incorporated as a low profileadditive component of a bulk molding compound, following the procedureof Example 3 . The bulk molding compound was then molded and tested asdescribed in Example 3. The molded panel, prepared in this manner had auniform red color. Shrinkage during molding was found to be 0.32 milsper inch perpendicular to the ribs and 0.75 mils per inch parallel tothe ribs. Surface profile was 233 microinches per half inch, averagedover a 2 inch span in the center of the panel and 150 micro-inches perhalf inch over the 3/8 inch rib.

EXAMPLE 5

A cross-linked vinyl chloride-2-ethylhexyl acrylate copolymer wasprepared following the procedure of Example 1, except that in place ofthe monomer composition shown, there was employed 150 parts of vinylchloride, 50 parts of 2-ethylhexyl acrylate, and 1.5 parts of diallylmaleate. The resultant polymeric product consisted of 170 parts of afine, white powder and about 8 parts of larger, irregularly shapedparticles. Under examination with an electron scanning microscope, thepowder was found to consist of spherical particles having a diameter ofabout 20 microns with evidence of some agglomeration into clustersranging up to 200 microns diameter. The glass transition temperature ofthe cross-linked polymer was 69.5° C (taken as the mid-point of a 62° to77° C range). The swell index of the particles, determined in the mannerdescribed hereinabove, was 500%.

The powdered polymer, thus prepared, was incorporated as a low-profileadditive component of a bulk molding compound following the procedure ofExample 3. The bulk molding compound was then molded and tested asdescribed in Example 3. The molded panel, thus prepared, wascharacterized by a uniform red color. Shrinkage during molding was foundto be -0.06 mils per inch (very slight expansion) perpendicular to theribs and 0.88 mils per inch parallel to the ribs. Surface profile was259 microinches per half inch, averaged over a 2 inch span in the centerof the panel and 277 micro-inches per half inch over the 3/8 inch rib.

What is claimed is:
 1. A molding composition comprisingA. apolymerizable unsaturated polyester component; and B. an additivecomponent comprising discrete particles of less than about 50 micronsdiameter of a cross-linked vinyl chloride polymer having a glasstransition temperature of below about 100° C and which is chemicallyinert with respect to the polyester component and is swellable butinsoluble therein, said additive component comprising the polymericreaction product of vinyl chloride and at least one polyfunctionalmonomer.
 2. A molding composition according to claim 1 wherein thepolyester component comprises an unsaturated polyester and acopolymerizable unsaturated monomer.
 3. A molding composition accordingto claim 2 wherein the additive component is characterized by a glasstransition temperature below about 75° C.
 4. A molding compositionaccording to claim 2 wherein the additive component comprises thepolymeric reaction product of vinyl chloride and about 0.1 to about 10percent by weight of a polyfunctional monomer.
 5. A molding compositionaccording to claim 4 wherein the additive component comprises thepolymeric reaction product of vinyl chloride and about 0.1 to about 2.0percent by weight of a polyfunctional monomer.
 6. A molding compositionaccording to claim 5 wherein said polyfunctional monomer is diallylmaleate.
 7. A molding composition according to claim 4 wherein theadditive component comprises the polymeric reaction product of vinylchloride, at least one monofunctional unsaturated comonomer capable offorming a linear homopolymer having a glass transition temperature ofbelow about 80° C, and a polyfunctional monomer.
 8. A moldingcomposition according to claim 7 wherein said monofunctional unsaturatedcomonomer is present in an amount of less than about 40 percent byweight, based on the total weight of additive component.
 9. A moldingcomposition according to claim 8 wherein said monofunctional unsaturatedcomonomer is a monomer capable of forming a linear homopolymer having aglass transition termperature of below about 0° C.
 10. A moldingcomposition according to claim 9 wherein said monofunctional unsaturatedcomonomer is selected from the group ethyl acrylate, n-butyl acrylateand 2-ethylhexyl acrylate.
 11. A molding composition according to claim10 wherein said monofunctional unsaturated comonomer is 2-ethylhexylacrylate.
 12. A molding composition according to claim 11 wherein saidadditive component comprises the polymeric reaction product of vinylchloride, 2-ethylhexyl acrylate and diallyl maleate.
 13. A moldingcomposition according to claim 12 wherein said additive componentcomprises the polymeric reaction product of vinyl chloride, 2-ethylhexylacrylate, 1,3-butylene diacrylate, ad diallyl maleate.
 14. A moldingcomposition according to claim 4 wherein the additive component ispresent in an amount of about 5 to about 45 parts by weight per 100parts of polyester component.
 15. The composition according to claim 14when polymerized to form an infusible product.